The alcohol dehydrogenases, ADHs, have been pivotal to the development of enzymology and have widespread applications. Liver ADHs have been the primary focus of investigations and show broad substrate specificity, oxidizing alcohols from methanol to steroids. They also have the ability to oxidize aldehydes to acids. This activity is not widely recognized, although there have been sporadic reports in the literature of related phenomena. The prevailing view, however, is that the reported kinetic values for both aldehyde oxidation and aldehyde dismutation preclude the physiological relevance of this reaction. The core of this proposal is that horse liver alcohol dehydrogenase, HL-ADH, is not just able to oxidize aldehydes as an intriguing, albeit nonphysiological side reaction; but when assayed under conditions that do not obscure this activity it is fully competent to catalyze the oxidation of aliphatic aldehydes to acids with catalytic efficiencies comparable to and even much greater than its catalysis of alcohol oxidation. Moreover, that essentially all previous kinetic and mechanistic investigations conducted on alcohol dehydrogenase-catalyzed aldehyde oxidation are flawed on any of a number of grounds. As will be discussed, the true abilities of HL-ADH have been masked by: i). a failure to observe the rapid dismutation of aldehyde to acid and alcohol prior to the net generation of reduced pyridine coenzymes, ii). the inappropriateness of the kinetic analyses used to compare reactions, iii). the near exclusive use of changes in A340 (NADH concentration) as an indicator of reaction progress, without monitoring time-dependent changes in the concentrations of other reactants or products; iv). the unrecognized impact that aldehyde oxidation has had on measurements of the kinetic values for alcohol dehydrogenase-catalyzed reactions, and/or v). the chemical reactivity of amine-containing buffers toward aldehydes. Finally, the ability to conduct the facile oxidation of aldehydes to acids is not confined to the liver alcohol dehydrogenases; this ability is shared by other, mechanistically distinct alcohol dehydrogenases. Our investigations focus on the biochemical and enzymological aspects of the ability of alcohol dehydrogenases to oxidize both alcohols and aldehydes with comparable efficiencies, with specific emphasis on their ability to conduct sequential oxidations. As we obtain more information on the ability of alcohol dehydrogenases to oxidize aldehydes, we will compare their structures with ADHs that do not readily oxidize aldehydes. The Computer Graphics Laboratory will be used to interpret the structure/activity relations and interpretation of sequence analyses of related proteins.